


Maybe-Sorta-Unhealthy Co-Dependency Time-Traveler’s-Club Membership Thing

by HazardousFancy



Category: Undertale (Video Game)
Genre: Adult Frisk (Undertale), Cunnilingus, Ecto-Penis (Undertale), Ecto-Tongue (Undertale), Established Relationship, F/M, Female Frisk (Undertale), Fluff, Fluff and Smut, Interspecies Relationship(s), Introspection, Oneshot, POV Sans (Undertale), Papyrus (Undertale) - Freeform, Secret Relationship, Smut, Technically?, Toriel (Undertale) - Freeform, but it really doesn't matter lmao, for all intents and purposes they're just body parts hahaha, gray ace sans?, i leave frisk's age ambiguous but it's implied pretty heavily that she's over 18 lmao, kinda idk, like it's just what sans has but i don't make notes about it or anything, like it's there but it's not really a focal point, mentions of... - Freeform, same with, thought i'd tag just in case
Language: English
Status: Completed
Published: 2018-11-20
Updated: 2018-11-20
Packaged: 2019-08-26 10:12:39
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 9,342
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/16679659
Author URL: https://archiveofourown.org/users/HazardousFancy/pseuds/HazardousFancy
Summary: My shot at some Frans... Mostly Sans ruminating on his relationship with Frisk, and then they fuck a little bit for good measure, and then Sans falls sleep and Frisk goes to watch a movie with Papyrus. It's dirty, but like, not /that/ dirty.





	Maybe-Sorta-Unhealthy Co-Dependency Time-Traveler’s-Club Membership Thing

The situation they were in would probably look pretty strange to anyone who had the misfortune (or luck? It certainly wasn’t an easy feat to catch Sans and Frisk ‘in the act’, it’d be worth bragging about, maybe) to walk in on them. The room was poorly lit, and smelled just a little too strongly of french-fry grease. The sun was setting outside an open window, the room was quiet, cars could be heard from a highway somewhere in the distance, and Sans sat nearly motionless while Frisk partially undressed him, but not with any kind of eagerness or lust, just… The standard way. Unzip hoodie. Pull it off arm-by-arm. One slipper, then the other. Then the socks. Both of them relaxed in the bed created by all of the clothes on Sans’ floor; and she was concentrated on her task, not even looking at Sans’ face to see if this was somehow turning him on, just diligently, carefully removing the clothing items one-by-one, DETERMINED to be thorough, apparently. And she wasn’t missing out, Sans’ face didn’t show any particular emotion, other than his usual permanent smile. He watched her take clothes off of him with a look of almost complete disinterest. To anyone else, it might have looked like Sans was basically acting like a little kid who Frisk had to undress because he didn’t know how, or a doll, or someone too sick to do it themselves. Alternatively, their friends could probably conclude that somehow, someway, Sans was actually SO lazy that he’d convinced Frisk to undress him, and soon he would kick her out to go take a shower or something.

Rather than that they were undressing because they were about to have some kind of sex, which they were. Unless they got distracted or fell asleep or something, both likely possibilities. Sans wouldn’t have the process happen any other way, but he couldn’t pretend he thought this looked like standard foreplay.

Though Sans and Frisk were kinda strange to begin with. Maybe. Sans had always considered himself a pretty average guy. Maybe about as average as guys come, skeleton or otherwise. But at this point he’d be really crazy not to conclude that, _just_ maybe, his life experience had been sort of unique up until this point. Not that it still wasn’t unique, just more like, in a good way? And that weirdness pretty clearly extended to how this thing with Frisk came to be. Not weird in the fact _that_ they came to be, no way. That, in retrospect, felt inevitable. Weird in like, the best way. Weird in the way that Sans felt really, really lucky to have Frisk exist to keep him company and not force him to talk. That he’d had her to work with him to get the ‘happy ending’ neither could do alone. Had her promise to keep all his secrets with the most affirming silent thumbs-up he’d ever seen, to share hers and put all her faith in him like she was simply trusting him with a care package, though Sans knew undoubtedly that her secrets were just as precious, and now, have her to take off his clothes and hum a little tune to herself like this was just some kind of laziness-enabling daily ritual, when, to them, it was definitely a precursor to sex, but probably would be pretty hard for outside eyes to guess this far ahead. Pretty hard for outside eyes to figure out they even had this kind of romantic… sexual… nap buddies… relationship in the first place.

...Sans wasn’t entirely sure of that though, at least, regarding their friends and family. How much were they aware of the extent of Sans and Frisk’s relationship, right now. Like, he knew nobody _knew_ they were, heh, _boning;_ but whether or not they would be surprised to find out… He really had no idea. Sans was good at understanding other people's’ perception, especially of himself. He knew how to pretend not to be super depressed. He knew how to hide his fear. He knew how to control his enthusiasm. Feel his hope sparingly. Controlling situations like that was pretty familiar to him. But he had to admit, he wasn’t all that practiced at keeping something like _this_ under wraps. Whether or not he was succeeding as much as he assumed he was, he wouldn’t put money on it.

“Something like this” being… His affection for Frisk? Attraction to? Admiration for? ...Dependence on..? Whatever. The ‘girlfriend’ stuff. If there were tells that he and Frisk were, like, a ‘thing’ now, he wouldn’t be able to say with confidence he could catch all of them before they slipped out. But from what Sans understood about romantic relationships (which really wasn’t much) his and Frisk’s didn’t really share all that many traits with the majority anyway; so who knows? Maybe that, Sans’ private nature and Frisk’s silence were already more than enough to keep their little secret a secret. Maybe.

After she’d gotten him down to his shorts and T-shirt, which was usually enough for the two of them, and she’d taken off her big ol’ colorful sweater and pants, and each of the clothing items were now basically lost to the sea of garbage and dirty clothes already on the floor around them, he happily accepted the lanky, half-naked girl into his lap. And... he didn’t really shower her with affection or anything. He wasn’t sure he really even knew how to do that, not that he ever tried, at least, not like in the movies. It seemed kinda tiring, and a waste of time, when he would rather just sit here, resting his head on her shoulder, turning his face so his teeth were against her throat and he could feel her pulse there, her squishy chest against his ribcage, one bony arm around her waist and pulling her tighter into him, under the half-guise of making it easier for him to lay against her rather than promising any kind of heated passion.

Sans almost never actually initiated any clothes-taking-off, it was fun to watch Frisk do it for him with her special brand of quiet anticipation, and to know that she was the one making the choice to take the next step. Or maybe he was just really, really, _really_ lazy. Or maybe he wanted to maintain the illusion that he didn’t care one way or the other, and was mostly doing all this just to make her happy. He had a complicated relationship with letting himself be passionate, letting himself care, and an even more complicated relationship with _showing_ it. Not that Frisk ever expected much of that from Sans in the first place, but reminders seemed okay, especially because sometimes he did have bursts of energy for her. Sometimes. It just wasn’t common, just wasn’t who he was.

And she never complained one way or the other. He suspected she liked being with him to be with him, to make him feel good, to get her kicks with him because she trusted him enough to help her out, rather than because he was a particularly passionate lover (and even on his passionate days, he was sure he wouldn’t make the cut for that title anyway), and the knowledge that it was her love for him that made her want to take him to bed made his soul burn with warmth more than any kind of afterglow of an orgasm or anything superphysical like that.

Though he’d learned to quite enjoy that superphysical stuff, lately. He loved the warmth of just being Frisk’s chosen emotional anchor, her precious object of affection. But he wouldn’t mind (I mean _really,_ **_really_ **wouldn’t mind) more of that less important, dirtier kind of warmth, from her too. If she wanted to do the work, of course.

Still, in true Sans fashion, he didn’t push to get her to do anything more there between his legs. He just played with the hem of her shirt and bathed in the warmth of her body and she was sighing, happily, instinctually, just a little, in a way that he was sure only he ever heard. Her hands rested delicately on his back, and it might have seemed like she, too, wasn’t all that into it - sitting there limply in his arms - but Sans knew her much, much too well. The way she tilted her head back, ever so slightly, let him see her breath catching in her throat. The way she dipped her head down so her hair parted to let one golden, shining eye catch his flashing one. The way she leaned into his touch, scooted closer into him, centimeter by centimeter. Sans wasn’t much of an initiator, but Frisk, somehow, in all her silence and peaceful resignation to most things in life, was always happy to be. Blink, and you’d miss it. But Frisk had always been an expert flirt, and even without all that much of a reaction from the perpetually-smiling skeleton beneath her, he knew she knew exactly what she was doing to him.

And, honestly, Sans wasn’t sure why or how. Not really. When it came to more impressionable people, monsters, rocks, it was easy to see why Frisk’s attentiveness and charm could fluster them. But Sans was… Sans. Before Frisk was grown, Sans had never thought twice about romance. Sex, affection, whatever. All that junk. Just wasn’t really his style. It still wasn’t, for the most part. He never got jealous of couples. Never swooned over romantic movies. Flirting, even Frisk’s playful style, sometimes, just made him uncomfortable; and he was excellent at deflecting that kind of thing. Sans didn’t even really get lonely. Not like some people did. He was content to spend his days lazing around, minimal contact with others, milling about, staying out of the way. He’d downloaded a dating app once on his phone, and it took so much effort just to open the thing he was immediately exhausted. It didn’t stay for long, deleted without a second thought to make room for more pictures of blank patches of dirt, the backs of strangers heads, and things he thought were pretty funny or weird or gross, even if he was sure nobody else would ever want to see them. Except maybe Frisk. Frisk. Frisk.

True to that whole ‘we’re conveniently quiet’ habit they shared, the current situation was pretty stable, if Sans did say so himself. Frisk had come over for a movie night, and that really had been the plan, no innuendo; but they hadn’t yet informed Papyrus. Frisk was so quiet, surely he didn’t even know she was in the house yet, and probably wasn’t sitting in the kitchen below thinking ‘gee, I wonder if the Human Frisk and my brother are getting inappropriately cozy above me?’ Papyrus wasn’t stupid. Sans was sure he would put the pieces together eventually, but today they certainly hadn’t given him any hints so far.

Not that Sans _actually_ wanted this to be a secret. Though Frisk wanted it to be a secret even less. Not that he thought Frisk was one to send out fliers about their new status as a romantic couple (though, knowing how unpredictable Frisk was… hmmm…) it wasn’t like they would ever be particularly public with their affection. It just wasn’t their style. But when Sans dodged tricky questions, or Frisk had to lie for him, he could tell it hurt her. Just a little.

It wouldn’t be a secret forever, it just couldn’t be… But he didn’t exactly have a cunning plan for how to put everything on the up-and-up anytime soon either.

There were a lot of reasons he wasn’t prepared to tell their friends. He’d known her since she was a little kid - probably the most obvious one. He also wasn’t really sure how old she was now. Human ages were weird. He knew enough about the surface that there were some kind of legal whatevers about ages and consent and all that up here - not that that wasn't also true in the Underground, but Sans had never really thought about it, because he’d never had any reason to. Wasn’t relevant to his life. Now that he had a reason to consider it, he still didn’t, really.

Of course, he knew she’d had a thing for him for a long time, a little crush, not sure when it started, but long enough ago that it was old information, and it didn’t mean anything to him. Frisk had endured lots of other crushes of her own, requited and unrequited. And it’s not like he had to resist his attraction to her when she was a teenager (and she had been an awful, unpredictable teenager, as most teenagers seemed to be, human or otherwise) because he wasn’t attracted to her then. He was sure he never would be. So sure, in fact, he never had to convince himself, or anything. Never had to defend himself to himself. He just wasn’t. He was never really attracted to anyone in the first place. No matter how cute Frisk was as a teenager, no matter how much trouble she got into, or how inappropriate she was with him (Frisk pushed boundaries with everyone) he never felt any kind of weird human-fetishy lust for her. She never forced him into any weird situations either. Didn’t try little tricks like she did on other, um, victims of her charms? She barely even flirted with him, even compared to her own mother, she knew him too well to force that on him, and it was just no big deal, so he didn’t worry. Sans had been 100% sure that her feelings for him were puppy love, they certainly didn’t interfere with their friendship, and Frisk was a popular, flirtatious, romantic little dude indeed. (Though she’d been significantly taller than him for years… she still kinda gave off that ‘little shit’ vibe. ...Something he admired about her.)

So when Sans realized he’d actually invested feelings in her, when he realized her innuendos actually were turning into pictures in his head, when he realized he wanted to touch her more than what was appropriate, (not even in a dirty way, just like, the back of her neck… Her shoulder blades… The small of her back… Okay, maybe it _was_ in a dirty way but this was new to Sans, give him a break,) when he realized it was frustrating and anxiety-inducing to go too long without being around her, especially when things weren’t going so great for him… He didn’t know how to deal with the information. He just felt what he felt. He couldn’t not. Before it all started for him, when Sans thought about Frisk’s future, he saw her with a lucky partner, but he could never have guessed he’d want that role for _himself_. But he did. He really, really did.

He wasn’t _that_ gross, or stupid, or insensitive. Actually wanting Frisk back was genuinely a huge surprise to him when he realized it. Like, a really big, giant, super-shocking surprise. And maybe he’d been driven a little crazy about it at first. Like, he didn’t know he _could_ want anyone like this. The fact that when life did decide to inform him he could, in fact, want someone enough to care, and it was for the kiddo after all, Tori’s daughter, his closest pal who he’d known her whole life… He’d be lying if said he’d slept soundly much those first few months. At least he could say he was tossing and turning because of romance-anxiety rather than existential-dread-anxiety. At least on the nights he forced down some sleep meds he didn’t have terrible, cripplingly horrifying nightmares as a result of what was plaguing his mind. No, no nightmares, just nice, wonderful, sweet, sweet dreams about Frisk. And Him. And him and Frisk. And Frisk and him. Pants optional. And maybe he woke up feeling guilty before he realized how fated it all was, but that was as bad as it got, so like, not the worst experience of his life, confusing and difficult as it might have been.

Even accepting that he wanted her like he did - like he does, he’d definitely resisted this stuff at first. Resisted caring about the distinct, greasy, unevenly-shampoo’d smell of her frizzy hair when she lay her head on his shoulder. Resisted shivering when she slid her hands into his sweatshirt on a cold day, tried to try to remind her that she definitely had mittens in her pocket. Resisted having opinions about the clothes she wore, whether or not they looked ‘Frisk’ enough, or, of course, whether or not he could see her body all that well in them. Resisted letting her jump into  his bed with him when she was over too late to go home and sleep, as much as it always felt like _such_ an amazing idea, and, simultaneously, the _worst_ idea ever. He never had any illusions that these feelings didn’t have consequences. Thing is, Sans was pretty good at staying out of trouble. One of his specialties. And he had been sure this funny, uncomfortable, way-too-comfortable view of Frisk he developed was going to pass, especially because he didn’t really recognize these feelings right away in the first place, but they didn’t pass. And Frisk...  Before all this, he’d been sure she’d easily find someone that really made her heart happy, and she would fall in love forreal, and either realize her feelings for him were silly, or forget she ever had them in the first place.

But… That didn’t happen. And, he’d never said this out loud, (though he was sure Frisk would get it out of him eventually - she always did. Secrets? What were those? With Frisk in his life, he wasn’t sure he had a concrete definition anymore.) But now the idea of her “finding” anyone else, anyone else making her heart happy, her soul, made him feel sick. When others reacted a little too much to her flirting, he had to pretend to himself that he didn’t even see it. When the rest of their family poked their heads into Frisk’s love life, suggested she see someone, set her up, it felt like betrayal, as if the romantic development in their relationship was even known to the others, which it wasn’t. Yeah, it seemed irrational, but she was **_his._ ** He was **_hers._ ** It was a universal constant. Not something they’d ever said explicitly to anyone, even each other, but just the thought of her giving even a little of what they shared to someone else was maddening. The idea of her leaving anyone else’s bags of chips out to get stale to eat because that’s how she liked them, and pretending it was an accident… the idea of her rummaging around in someone else’s secrets, learning too much about someone else’s well-buried, complicated history... the idea of her delicately touching the inside of someone else’s ribcage, like it was the most important task in the world... the idea of her running to anyone else with the thoughts that plagued her mind - her misery so much more well-hidden than his would ever be... the idea of her talking to anyone else the way she did to Sans - beyond the timeline stuff, even. Just friend things. Best friend things. Love things. Life things. Just being. Through all timelines and all struggles and all dreams and nightmares, Frisk was his, because the universe wanted it that way.

...Okay, maybe it was just plain, old fashioned jealousy. Maybe it had nothing to do with obeying the laws of the universe. Sans had never been that good at that in the first place, so maybe this level of emotion was actually kind of normal, for people who cared about their partners the way he cared about Frisk. A chilling thought, that maybe people weren’t actually exaggerating about romantic love all this time like he suspected. Maybe wanting someone was really just this overwhelming for everyone. Stars, he hoped not. As if the universe wasn’t chaotic enough.

Well, it didn’t matter. Those thoughts were few and far between. Ever since Frisk had finally taken him to her bed (or, actually, their first, like, real, _third-base_ time was on his couch - if he remembered right. Oh, who was he kidding, he remembered every detail. Yes, it was on his couch; yes, Pap came home to the half-dressed pair and they had to come up with an excuse on the fly; yes, he felt like she’d lured him into a trap, and no, he didn’t regret it for one second.) she’d never given him any _reason_ to be jealous, or worry that she wasn’t as invested as he was... which was actually pretty crazy, since for the longest time he’d rejected her. If she doubted his commitment to her, he wouldn’t blame her, or at the very least, couldn’t expect her not to give him shit for it once in a while, after years and years of her mentioning how she’d marry him someday, and Sans just ruffling her hair, and saying “haha, yeah kiddo. sure you will. and i’m gonna be the first monster president.” But no, Frisk went out of her way to make the ‘love game’ stuff easy for him. Or maybe it was because they were already so close, he and Frisk didn’t really do misunderstandings in the first place. Or obligation. Or expectations. But Sans still hadn’t been sure what to expect from a romantic relationship, even with the easiest person to be around he’d ever known in his life. Other than the ‘unsure and hiding because maybe this wasn’t super appropriate’ stuff, which was ultimately his choice, it was seamless.

One time, he did look at her driver’s license, out of curiosity to see how old she was, but then he didn’t actually bother to look up if that was in the legal range or not. With Frisk it just didn’t matter, he knew that. Which was kinda weird. With Papyrus, Sans kept careful track of his age. Birthdays and allowances and all that - one year was a big deal to Papyrus. It was a big deal to Sans, for Papyrus. But for Frisk…? Even if he wasn’t more than aware that the timelines must have messed with her life experience, she was just… Timeless. Haha, timeless… Timelines… That wasn’t terrible, maybe he could refine it into a real joke later.

Anyway, point was, he didn’t really care about her age. A few months ago, before all this touchy stuff started, he’d visited her dorm room, one of many times, but this time was kinda different somehow. She still technically lived with Tori, but she had her own space, and she had piles of homework, and not-homework, and a closet full of snacks, and a weird, mismatched, but mostly only practical bedding setup, and souvenirs, and photos, and he realized she had put this all together herself. Tori’s influence was long since buried under Frisk’s hoarding (kleptomania..?) habit, and he realized she could do anything, not that he didn’t already know that, just like, she was this whole person, who could do anything in the world, anything in the universe, and she _let_ him, Tori, Asgore, Undyne, Alphys, Papyrus, into her life. If this kind of independence was unusual among other students her age, he didn’t know and he didn’t care. Frisk was Frisk. Frisk was quiet, and decisive, and headstrong, and thoughtful, and her own person, wholly, completely, and it wasn’t like Sans had been hit with some kind of love realization at that time or something. It was really just another day. But looking back, at least, he was sure that if on that day she had pulled him down onto that pile of books and clothes and useless crap, and kissed his face, and took off his clothes, and whispered to him some simple, dirty commands into his ear canal; his only request would have been ‘lock the door’.

Was he really super hot for a kid he’d basically help raise, like a sicko? Did he get off to the idea of banging his best friend’s daughter on the down-low? Did he take some kind of perverse satisfaction in having this kind of power over someone who was once his enemy? He didn’t really like any of those ideas, though none of them felt all that wrong either. Was he really invested in someone he’d known and cared for, for so many years? Did he feel safe and warm in the arms of someone only Toriel could raise to be so sweet? Did he take comfort in holding Frisk tightly in his grasp, knowing she was really here, this was really real, and she was really Frisk, and he was really Sans, and Chara was somewhere else, probably with that shitty little plant, and they were probably making trouble for someone else now, and he and Frisk were alone together at last, and there was no malice, no resentment, just a soft but unbreakable connection between them that could be tested a million times over and never budge, he knew, and this timeline was more permanent than he could have ever hoped for, and nothing could ever take her, or this world, or the memories they made, away from him, without a fight? Well… He could live with some of those, he guessed. Maybe a little weird; not to just like someone because you liked them, but, eh.

Before Frisk, Sans had been almost sure he wouldn’t ever really ‘fall’ for anyone, but with Frisk, _for_ Frisk, he did. And if that had partially been encouraged by their maybe-sorta-unhealthy co-dependency time-traveler’s-club membership thing, well, it didn’t bother Sans. Frisk was awesome. Being in love was awesome. If it had taken going through hell with her to form a bond so strong, then, like, damn. Good. He couldn’t think of a better reward for all the pain they’d  been through than for them to have something so deep and unbreakable between them. And also, sex. That was pretty cool. Again, Sans had been pretty sure sex with other people wasn’t worth the effort. Like, masturbation was fine, sure. Just taking care of business. Before trying it with Frisk, really, he couldn’t really understand wanting to physically pleasure another being enough to both be all naked and vulnerable in front of them, and then also put in the physical and mental work. It seemed like a major waste of time and effort. Or at least, it had… Before… But with Frisk… _Stars._ Sans didn’t feel so left out anymore, when people talked about how nice sex was. He still would rather talk about basically anything else, conversation-wise, but, like, he _got_ it, for the most part.

He was scared of their friends finding out, nervous about what this meant for the future of he and Frisk’s relationship, confused about why he felt the way he did, and he really didn’t know what the future held for them; but guilt was missing from the equation for sure. It was hard to feel guilty when it felt so good, so freeing, so right. That is, he was pretty sure she was his soulmate, if that was a thing. He was pretty sure he was hers, and he was pretty sure she knew it too. She never worried that she was an unconventional lover to him, because she was, and he loved her for it; so Sans didn’t worry either. They did what came naturally to them.

In this case, it was Frisk drawing intricate lines all over his bones with her fingers, through his shirt. Sometimes they took off all their clothes, but mostly they didn’t. They rarely went hard enough to get any sort of workout. Too much effort to have to put them back on later, as well. At the moment, their clothes also protected them from the dirty carpet, a little. It wasn’t that they didn’t like to see each other. Sans was sure if he hadn’t seen Frisk totally naked by now, he’d be crazy, even after having regular sex with her. The curiosity, at least, would be torture; and if she didn’t like to look at him naked, then all the time she’d spent memorizing the arrangement of his bones was very strange indeed. But they didn’t need a refresher every time. No, that’s not what this was about. This wasn’t about how sex should be had, how it was expected to be had; this was about what they wanted to do. Nobody else.

Neither of them spoke a word. Frisk continued her incursion with more gusto, touching him with familiarity and curiosity all at once, unafraid and exploratory. Her hands explored his whole torso, fingers drawing lines all over, lingering everywhere she went, as if this was the first time he’d ever let her touch him. Her fingers traced his eye socket, over the bridge of his nasal bone, down his cheek and to his teeth, where she poked gently, but insistently at the place where they came together, a silent request, and he obliged, opening his mouth a little for her fingers to slip inside, but not before materializing his tongue so he could play too. He ran the tip of it under the pads of her fingers, exploring the abrupt texture change from her flesh to her smooth fingernails that were probably dirty, but like, whatever. She just watched his teeth, as if she could see inside his mouth, and blushed, her breathing becoming shallow. If that wasn’t enough, finally she made eye contact with him, blushed a shade darker, and Sans had spit out her salty fingers so that he could adjust himself where he sat, and fiddle with his shorts before leaning forward to press his teeth to her mouth with his own silent request, letting his tongue prod at her lips, slip between them and run over her slimy, closed teeth before she opened her mouth to allow him inside. Immediately he was exploring her mouth. Her weird, hot, kinda gross and super wet mouth. It was so surreal how her cheeks created these little barriers between her jaw and the outside world. So, so surreal. Her mouth didn’t taste all that good, hadn’t brushed her teeth before coming over, apparently, but more than that, somehow her mouth just _felt_ cute to his tongue. She didn’t whimper or moan, even though he knew she could, and did, to get under the skin of others, but Frisk didn’t put on a show for Sans. No, nothing but complete sincerity. The real stuff. Her breathing through her little nose was uneven and shallow, her mouth was eager against his own, and when he briefly opened his eyes he could see her furrowing her brow with passion and she was so, so cute, and she looked so, so happy, and he couldn’t believe how much his weird magic tongue in her gross human mouth made her so happy, but it did. It made him happy too, which was no less of a mystery. He wasn’t in the mood to analyze anymore, though.

She turned her gaze back up to his face where she looked him in the eye with what he could only describe as longing, and in a moment of uncharacteristic, embarrassing exposure, his breath caught in his nonexistent throat, which was probably pretty weird looking when on his face remained his casual smile. Maybe it wasn’t so bad, though, because hearing it made frisk tilt her head down, give him a wicked grin from underneath her bangs. It wasn’t much of a noise at all, but like Sans could see underneath Frisk’s collectedness, she could see underneath his carelessness, and he knew that, despite the nonchalant look on his face, casual posture and unwillingness to help Frisk prepare the both of them - How he subtly avoided eye contact to decrease his chance of blushing under her gaze, how earlier he had moved his arms and adjusted his position to make taking his sweatshirt off him easier, his soul glowing in his chest, just barely, through his t-shirt… It was more than enough to tell Frisk everything she needed to know. One of the many reasons Sans had never really pursued romance. He just didn’t have the temperament for it. Enthusiasm was the key ingredient in all that stuff, and he had very little of it to spare. With Frisk, though… With Frisk… He didn’t try at all, and somehow, she still seemed to find everything she wanted within him.

Pleased to hear the little reaction, Frisk wrapped her arms around him, and slowly, deliberately let herself grind her hips down against him, and she made a little squeak sound, and Sans would have liked to bury his head in her neck and let her work him up without looking at each others expressions, but she held his face in her hands, and looked straight into his eyes, and finally, blue blush conquered his face, and his smile wavered, which she’d definitely been waiting for. Her own grin spreading across her flushed face.

He kinda forgot that. Forgot that she liked to get a reaction out of him like that. Kinda always forgot it. As sure as he was that they were meant to be together, he wasn’t super duper sure what Frisk actually saw in him. On some of his worse days, he was really, completely sure that anything she saw in him were traits she had made up in her head. But lucky for him, Frisk was a very physical person, and this was a one-to-one. He smiled, she smiled back. He hugged her, she relaxed. He moaned, she trembled. Partner-choosing-logic aside, she cared about him, was comfortable with him - was _attracted_ to him, like, really really attracted to him, and she showed it. And he really didn’t know why she could make him react like this - make him show her expressions he was pretty sure their friends wouldn’t even believe he was capable of making - if it was because of his lack of familiarity with sexual situations? Or because his body was just that responsive to her in particular? Or maybe, because even though it still made him feel kinda uncomfortable and exposed with his usual apathetic demeanor broken, it also felt like it was one more thing on the long list of things that he could do differently with Frisk. Before getting close to Frisk, he didn’t talk to anyone about his feelings, ever. Before taking the chance to rely on Frisk, he didn’t trust anyone to do anything. Before he knew he loved Frisk, he was sure the good/bad balance in the universe was more or less even, approaching ‘mostly bad’, and now he was sure there was more good than he could have ever seen before. Before he started sleeping with Frisk, he was pretty sure he’d only ever moaned with pleasure like, a handful of times in his life. And certainly never the way he did with Frisk, when she got him to that level of vulnerability. Grateful and sincere.

He’d entertained the idea that all of this was unlike him, at one point, because it was, but it never felt like it was, he realized. It felt weird and scary and surreal to act on it, but he always had feelings to talk about, wished he had someone to trust, hoped that there was more good in the world than he could see in front of him. The sex stuff was a surprise, he never knew he wanted anyone to hear him moan, but, well, you learn something new every day, huh?

He wanted Frisk to hear him moan, but he didn’t really want to hear himself moan, kinda weird. He’d rather wait until he was distracted enough not to care, and, despite the tight shorts, he wasn’t there yet. With a whole bunch of these things, talking about his feelings, whatever, it wasn’t a switch he could turn on. It never would be. Trusting someone, investing in someone, even Frisk, none of this would ever be his ‘thing’, or whatever. But caring enough to be patient enough to indulge in all of it anyway - that could probably be his ‘thing’.

It was nice to have _future._

There was no rush.

So, in that vein, he gently pushed Frisk to lie down on the carpet, and scooted back so his head was between her legs with what he made sure was complete nonchalance, but he could feel her surprised, embarrassed, super-cute expression burning into the top of his skull; but it wasn’t until his tongue was out and dipping under the hem of her underwear that he actually looked up to see it. Her breath caught in her throat when his eye met hers, and he held back a giggle. For a moment he just sat comfortably on his elbows, watching his own knuckle stroke up and down where the fabric covered her slimier bits, and listening to her breathing get shallow again. Impatiently, she took off her own underpants, and tossed them aside, which gave him a little thrill, but after she shyly opened her legs for him, the first thing he did was to put his pointer finger right on her clit, and sing an off-key doorbell chime as he pressed it.

Frisk could always be counted on. She giggled and squealed a little, a much too kind reaction to having her lady bits arguably disrespected by the skeleton she loved. No matter how hard he tried, Sans could never kill a mood Frisk was set on. He could change it though, and it seemed he had, her laughter struck right through her shyness and she shoved his shoulder with her heel for a moment before catching him with her other foot and bringing him back down, her lanky legs tangling around his neck, and he found himself sort of smothered against the very part of Frisk she’d been hesitant to reveal before. When he wrestled himself free enough for him to look up at her face, she was giggling, her tongue out between her teeth in a nasty little grin that made his soul swell with pride and affection.

Responding to her silent order with an equally playful resigned expression, he started what he was down there to do in the first place, tongue exploring all the folds and wrinkles of her funky human genitals (that, really, he was attracted to, he assured her, but nobody could deny were also pretty weird.) He just kinda kept doing that for a while with no real urgency, her legs relaxing and freeing their grip on his head, and when her breathing became labored enough that it seemed to fill the room, he added two bony fingers to the procedure, sliding them inside her, all cozy and snug, turning his tongue’s attention pretty much exclusively to her clit, and she was gasping noisily, her face red and her body trembling and in an instant her insides grabbed erratically around his fingers, she squirmed where she lay over a decent amount of his own laundry, giving Sans a challenge of either following her movement or holding her hips down - both choices he found pretty enjoyable - her noises followed along with the motions of his tongue, the muscles of her thighs tensed, and his senses were overwhelmed by her climax before it ended, and Frisk looked so… Frisk.

She looked exhausted, it had only been a few minutes, but she had put her all into it, because of course she had. Her eyes were closed and when her breathing slowed she was smiling to herself. One could almost believe she had forgotten Sans was even there, the way she snuggled back into the mountain of dirty clothes beneath her.

Sans sat up, leaning on one arm and grinning at the satisfied girl in front of him, eyes lidded, soul heavy and warm. He just watched her for a moment, catching his own breath, trying not to act _too_ self-satisfied - not that she was paying attention. But that made her all the more endearing in the weak light of his dirty room. Acting in the way that came the most natural to her.

Not that Frisk didn’t have superego. She’d been in some sort of spotlight or other ever since she led the monsters out of the Underground; and was their representative in human affairs. Talking, understanding, _diplomacy,_ that was Frisk’s forte. Her flirting, her compliments, her insight, she was good with people in a way Sans was sure he would never understand. It was like she saw everything. Everyone. And she was good at learning just the right way to interact with people to keep them pacified.

But Frisk was also Frisk. Quirky and curious and _much_ more judgmental than any of her acquaintances might guess. Helpful and sweet and unapologetically _selfish,_ sometimes, in the best way. Quiet and coy and conniving. Wary and skeptical, but still too nice for her own good.

And this was what she gave to Sans. All of it, not just the parts she knew he would react positively to. Frisk was always herself with Sans. Maybe partially because of the same partial reason Sans was always himself with Frisk - they could see straight through each other anyway, whether that was what they wanted or not. But what didn’t happen anyway was them trusting each other with that power, trusting each other with their feelings and their bodies. Showing each other more than strictly necessary, more than they did to anyone else.

As if he needed to convince himself that the  image of his dear, beautiful friend breathing heavily, openly, sweetly, in just a camisole and nothing else on top of his gross clothes like she was in a bed with satin sheets, was a special sight. Heh.

She seemed so content and relaxed, he couldn’t resist. He let himself lay down next to her slowly, yawning, one hand under his skull, the other wrapping around her waist, and her eyes flew open. She turned to meet his face with a look of surprise. The source was clear, she was shocked he would want to just get her off and go to sleep right then and there.

He wasn’t sure why she was shocked. In fact, it seemed very predictable. But to assure her he wasn’t making a sacrifice, he grinned, pressing his forehead against hers. Still, he wasn’t surprised to see her face twist into one of defiant DETERMINATION, but he didn’t regret at least trying to catch some z’s.

She shot up, and yanked him to sit up again with her, holding him by the shoulders so he wouldn’t fall back down. He groaned exasperatedly, but finally reluctantly let his own spine do the work of holding him up. She gave him a look of incredulousness, gesturing questioningly to his, still pretty uncomfortable, shorts. He chuckled.

“it’ll go away eventually.” He shrugged.

“So wasteful…” Frisk grumbled, straddling his lap, and, okay, he had to admit, that sentiment sent a shot of lust through him that made sleeping right this very moment seem like a slightly less appealing idea. So he leaned back on his hands, and let her do as she liked.

What she liked was apparently to put her hand down the front of his shorts and take him gently in her hand, the other coming up to cup his cheek and keep his face focused on her own. If Frisk had tried this when they’d first started getting handsy, he would probably put up a fight against it, against letting her watch his face, depending on how convincing she was; but in the measure that he felt the need to wait a while before he really… well… gave himself to her. See and hear him the way she really wanted to. Well, the wait was contentedly over.

He gave her a breathless, nervous chuckle and a smile under deepening blue cheeks before giving her the okay with a wordless nod. Giddily, she began stroking him, and, yeah, he was as comfortable as he had wanted to be, but he couldn’t help it. He still closed his eyes, not wanting to watch her watch him. She didn’t object though; he knew she know just letting go in front of her was a big deal - a big sacrifice for Sans; and to her delight, he relaxed under her touch. He let her find a steadier pace, a tighter grip, and he was panting, his brow furrowed.

Keeping his eyes closed, he lifted one shaking hand to grab Frisk’s shoulder. He could hear her breathing gently, and practically see her satisfaction through his boney eyelids; and, as usual, he had mixed feelings. On the one hand, being this open, even with himself, wasn’t exactly his definition of fun. On the other hand, it felt good to be like this in front of Frisk. It felt good to be like this _for_ Frisk. And, of course, her hand pumping on him just a little faster every time she got a grunt or a moan out of him, _felt good_.

Maybe someday he’d really lose the anxiety that came with being so vulnerable or at least, a bit of it. So he could be as open with her as she always was with him, letting him watch her come undone with no reservations that he could pick up on, smiling and blushing and gasping without holding back, letting him experience all of her at her most delirious, just as he would have prayed she would.

But… Not today. He grabbed her wrist, panting heavily, and finally opened his eyes to look at her face.

“c’mere.” He requested, his voice dry and cracking beneath it, and with a warm, agreeable smile, she removed her hand, and came forward to lower herself on his lap. This time, he pulled the elastic of his own shorts down just a little to bring out his cock for a moment before pulling Frisk even further down on his lap and guiding it up inside her, out of sight as quickly as it had appeared.

She didn’t gasp, but her breath caught in her throat, and for a moment he wondered if he’d overestimated how prepared she was to take him, but before he could even finish the line of thought she began rolling her hips, moving quickly and eagerly on his lap, and his first thought was that he was glad she didn’t pull him down on top of her - missionary was exhausting. His second thought was that he was thrilled, elated, so content to have her wrap her arms around his shoulders and press her body completely against his, rocking feverishly and whimpering in his ear.

As often happened, Sans did overestimate one thing, which was how accustomed to this he was. This, bits rubbing together, was what he knew of as the most normal kind of sex; but connecting with her had him breathless before she even began moving. Maybe because she was human, and she was so hot and warm and fleshy, or because she was Frisk, his favorite person, his confidant, his other half, and she let him into her body and they were connected and nothing felt more right than this…

Or maybe he was simply hornier than he’d estimated when he was planning to go to sleep beside her without taking care of his arousal. Hm.

Well, whatever the reason, she felt like heaven, and she was grinding into him and doing basically all the work and if he didn’t have to hold himself up with one quickly tiring arm, it would be pure bliss. But it was pretty close, even having to keep himself from falling backwards, and with the free hand he grabbed the back of her top and pressed his face into her collar and now - _now,_ he let her hear him moan, for real. It was only fair. She was crying out in uneven bursts, gasping noisily in between, her pace only quickening now in response to the noises he let roll out of his throat and sink into her chest.

She tilted her head back for a moment as she moved her hips and went silent for a moment, looking ethereal, like he couldn’t believe she could possibly be getting this much pleasure from his body, but she _was_ , and it was hypnotizing, before she leaned forward again and grabbed his head, burying her own face in where her arm and his skull met, whining and moaning, moving faster and faster…

 _“Sans…”_ She hiccuped quietly, passionately, the sound of his own name so full of adoration, love, worship, in - just case he thought she forgot who she was riding; and now he was joining her, groaning with significantly less restraint - and significantly more volume, into the flesh of her chest, gasping and trying desperately to catch his own breath.

He tried not too sound to delerious as he pulled his face off of her for a moment to look up at her own sweet, overwhelmed face with glassy, lost eye sockets. “y-you gonna cum with me, kiddo?” He managed to ask dryly, in almost a whisper before he had to grunt against a particularly enthusiastic series of thrusts from her. The nickname was usually full of playful condescension, or regular condescension. The way he said it now, he might as well have called her ‘angel’.

“Mhm!” She confirmed, bit her lip and nodded forcefully before fighting her own passionate whine.

“kay.” He breathed, before switching the hand he was leaning on so he could bring his right down between her legs and rub her clit, gentle but firm, and she yelped; her gasping and moaning overlapping as she frantically rocked her hips, racing to the end, and Sans would have liked to chuckle at her enthusiasm - or her intense response to the addition of his fingers, which never failed to fascinate and astound him, but all he could do was whimper and moan into her with abandon, squeezing his eyes shut, moving instinctually up against her in time, and trying to focus on both his own orgasm - which was tipping over and making him release noises on the edge of being evidence of being overcome with pleasure that he would never admit to submitting in court - and his attempt to rub her clit, which he felt was akin to like patting your head and rubbing your stomach at the same time - an analogy that, Sans, at any other time, would use to mean ‘something not worth the effort’, but not this time. Frisk’s voice climbed in octave, though not volume, her movements desperate and frantic and he could feel her clamp down on him like she had on his fingers, cumming on him, because of him, for him, with him; and sure enough, they finished at basically the same time. Nice.

Still, between his concentration and his own climax ending, she had to grab his wrist and whisper a few breathless pleas, groaning to get him to stop rubbing her. He was more than happy to drop his hand, relax his wrist and just slump forward against her, joining her heavy breathing.

“shhorry.” The half-hearted apology was barely audible as he gasped quietly into the front of her shirt, and she giggled softly, her lungs rattling under his cheek, making him grin too.

She pulled his head back, still sitting on him, and this time he did not cooperate with her, letting her completely hold him up to look up at her with a look of exhaustion before pressing her lips against his teeth, which he allowed - for a moment.

After a moment, Sans groaned and urged her off of him gently. “sstoppp…” he whined exasperatedly, and with a mock pout, she obliged; freeing him, paying no real mind to the mess between them, and touching his sleepy face tenderly for a moment before, with a contented sigh, she laid back down on her makeshift dirty-clothes-bed, and he let his cock dissipate.

He adjusted his shorts a little before letting himself lie next to her again - this time, face first, with a strangled groan, muffled by a crumpled shirt; as if he’d just come out of a painful ordeal, rather than a pleasurable one. Exhausted, anyway. Frisk laughed at him, and was surprised when he lifted the hand closest to her for her to take, for comfort, or something, and didn’t raise his head to watch. She took his hand.

“You okay?” She asked curiously.

With his face still buried, his other hand came up beside his head to form a thumbs-up, and she laughed. After a moment, Sans was startled by the sound of skin slapping, turning his head out finally to see Frisk smack her own thighs, pushing  herself up off the ground and stretching, tall and still pretty naked and she was still gorgeous, but Sans was definitely done getting aroused today, body and soul.

“Welp.” She smiled, and Sans grumbled, annoyed at her for seeming rejuvenated by their sex, wherein here he was, like his life force had been half-drained. “Movie time?” She clapped her hands together and grinned down at the clearly tired, unresponsive skeleton at her feet.

Finally, he sat up, pressing a hand to his own eye socket to orient himself. “you expect me to sit through a movie after that?” He groaned.

She hummed tunelessly to herself for a moment, considering the question, and pulling her clothes back on - after using one of the many dirty ones on the floor to wipe up a little - and stood still for a minute, contemplating.

After coming to some sort of conclusion (though Sans already forgot what he’d asked) she reached down to pick him up by his arms, which was just ever-so-slightly humiliating every time she did it, but after a quick “hey-!” Sans gave in, and let her toss him onto his own bed.

“Nah.” She shrugged. “But I still want to watch a movie… I’ll tell Papyrus…” After pulling her sweater back on, looking pretty much as messy and cozy as before, she put her finger on her lips, thinking.

Sans spoke up sleepily, “if you’re really gonna go back down there”, he began with a yawn, “tell him you came up to get me, but couldn’t convince me to come down. any noises he heard were you trying to drag me out of bed.” and Frisk’s mouth twisted up. “You’re a good liar.” She admitted, folding her arms, as if she didn’t already know this well. Sans didn’t care about her judgement though, sincere or otherwise, and grinned at her from the blankets he was quickly curling up in.

“you love it.” he winked, then added “anyway, one of us has to be.” already closing his eyes.

He really couldn’t hear Frisk approach the bed slowly, but he could tell that she did anyway. “Goodnight sweet prince,” she half-whispered, and bent down to place a gentle kiss on the side of his head “And flights of angels sing thee to thy-”

Not bothering to open his eyes, he lifted one arm lazily to wave over his head, batting her away, making her giggle. “let me _sleep.”_ He groaned, and with one last chuckle, Frisk backed toward the door of his room. She opened it slowly, closed it slowly too, taking one last wistful look at the sleeping skeleton, and was only mildly surprised to see his hand twitch her direction, and murmur, “love you… dork.” before the phrase seamlessly turning into a string of metaphorical, but very audible Z’s above his head.

Sans wasn’t conscious to hear what she said in response, if anything, but that was okay. With Frisk, there was never any question.

**Author's Note:**

> I have a lot of experience with anemia/sleep disorder/hypersomnia/energy drain stuff, I always got the feeling Sans had some similar kind of medical condition, on top of the other fanon stuff. Also, his sexual/romantic history is up to you, coz I think it doesn't matter much in this case. If Sans was ever with someone else, it never meant as much to him as he felt like it should. Like, when you meet the right person, it doesn't really matter I don't think. He could have been totally inexperienced before getting with Frisk and it wouldn't really make much of a difference. Maybe he is. Up to you. Same with Frisk. Maybe Sans is her first, maybe not, whatever. They're determined to be each others last.  
> I don't think Sans' feelings would be controlled by numbers since he and Frisk like, live outside the bubble of reality lmaooo, so I don't say what Frisk's age is, but I feel like it's even more telling that Sans didn't "wait" he literally wasn't into it until she was an adult in the first place.  
> Frisk is female in this, but obviously not particularly feminine. She's just Frisk. She is what she is. If you really hate the idea of her being female, you came to the wrong oneshot lol.


End file.
